1. Field of the Invention
This invention pertains generally to methods and devices for assisting the flow of blood through the heart.
2. Description of Related Art
Congestive heart failure is a major global public health problem that results in hundreds of thousands of deaths and incalculable human suffering in millions of people each year. Current treatments included modern pharmacologic agents, automatic internal defibrillators and advanced pacing devices including synchronizers. These modalities offer some symptomatic improvement and, potentially, improve survival but all are palliative treatments at best and are not curative.
Existing therapies provide limited clinical benefits for patients in advanced stages of congestive heart failure. In fact, it is estimated that several hundred thousand patients each year with far advanced CHF experience only limited clinical benefit from existing well-established treatments, and could best be served by cardiac transplantation. Cardiac transplantation offers significant improvement in symptoms and survival for patients with end stage heart failure but is available to only a few thousand patients each year due to the limited number of donor hearts.
Mechanical circulatory assistance (MCA), in the form of a total artificial heart (TAH) or a left ventricular assist device (LVAD), has the potential to meet the needs of these patients with end stage heart failure for whom there is little hope. Unfortunately, mechanical circulatory assistance has not developed into a commonly used therapy in the treatment of heart failure.
Historically, there has been substantial evolution in the technology of mechanical circulatory assistance and changes in the paradigms regarding the efficacy of MCA and its role in the treatment of heart failure. The original paradigm envisioned the development of a mass-produced pulsatile TAH that could be implanted routinely in many hundreds of thousands of end stage patients who could otherwise benefit from cardiac transplantation. However, technical challenges have, thus far, precluded the development of the practical TAH needed to achieve the original vision.
Subsequently, it was proposed that LVADs could address the needs of most end stage patients and numerous LVADs have been developed in the last thirty years. Indeed, a number of effective LVADs have shown promise in clinical studies but have experienced only limited commercial success. Such devices include both pulsatile and rotary continuous flow pumps.
Clinical research has shown that LVADs have powerful hemodynamic effectiveness and offer substantial clinical benefit as bridges to cardiac transplantation and in treating post-cardiotomy shock. Recent experience with LVADs for destination therapy in patients who could benefit but are not candidates for cardiac transplantation, has demonstrated improvement in symptoms, quality of life and survival. Serendipitously, significant spontaneous recovery in left ventricular function has been observed in some bridge patients awaiting donor hearts. In some patients who experience spontaneous recovery of left ventricular function it has been possible to remove the assist device and delay or avoid the need for cardiac transplantation.
The phenomenon of spontaneous ventricular recovery in mechanically assisted patients who were thought to have a progressive irreversible pathology suggests some exciting possibilities. If significant left ventricular recovery can occur in patients with far advanced heart failure, perhaps the use of mechanical circulatory assistance in patients with less advanced disease could arrest or reverse the fundamental pathology of CHF in large numbers of patients. If such were the case, a radical paradigm shift in the treatment of congestive heart failure and the perceived role of left ventricular assist devices could take place. If a significant number of patients with CHF have the potential for reversing pathology, then the primary goal of the treatment of CHF could shift from the palliative treatment of symptoms to the treatment of the underlying progressive pathology in order to reverse the primary ventricular pathology. Ventricular assist devices could emerge as true therapeutic modalities rather than bridges to cardiac transplantation and palliation for end stage patients. Such a paradigm shift will require the development of ventricular assist device systems that requires much less invasive procedures for insertion than existing ones; specifically, systems that do not require a cardiac surgeon or cardiopulmonary bypass.
Intravascular transvalvular ventricular assistance has been used on a limited basis in patients and has demonstrated significant clinical benefit in the setting of acute cardiogenic shock, failure to wean from cardiopulmonary bypass, assisted high risk angioplasty and, beating heart coronary revascularization. More specifically, two non-thoracotomy methods for achieving central vascular access have been previously described and have been used to a limited extent in patients. These methods are transeptal cannulation of the left atrium and transvalvular cannulation of the left ventricle.
One previous disclosure alleges a method for cannulating the left atrium without a thoracotomy for total cardiopulmonary bypass. This method included placing a 7 mm cannula via the jugular vein through the atrial septum into the left atrium and placing a similar cannula into a peripheral artery. A pump was then placed between the two cannulae such that it withdrew oxygenated blood from the left atria and pumped it into the arterial system. This approach has been used to a limited extent to treat patients with acute cardiogenic shock, but has not been adapted for ambulatory or chronic use. Another disclosure has proposed a method for partial ventricular assistance which combines transeptal atrial cannulation with an implantable pump that could, potentially, provide long-term ambulatory ventricular assistance.
Still another prior disclosure proposed a novel non-thoracotomy method for cannulating the left ventricle to implement prolonged ventricular assistance. This method required placing a 5 mm cannula via the carotid artery retrograde across the aortic valve into the left ventricle. The aortic valve leaflets provided a seal against leakage of blood around the inlet cannula. A similar cannula was inserted into a peripheral artery. A pump was then placed between the two cannulae such that it withdrew oxygenated blood from the left ventricle and pumped it into the arterial system. It has been proposed that the subclavian artery in the human could be used for insertion of the transvalvular cannula and the pump outlet connected to the subclavian or femoral artery. Subsequently disclosed embodiments of this approach employed external roller pumps or rotary pumps. However, these embodiments are not generally considered practical for ambulatory or chronic clinical use.
One previously disclosed LVAD system was intended to adapt peripheral transvalvular cannulation of the left ventricle to a miniature (6.5 mm) intravascular blood pump (Hemopump®). This method required insertion of a high-capacity axial flow blood pump into the femoral artery. A flexible inflow cannula attached to the pump was guided retrograde across the aortic valve into the left ventricle. The outlet of the pump was located in the thoracic aorta. Blood was withdrawn from the left ventricle and pumped into the aorta. Power was supplied to the pump via a percutaneous flexible drivecable which was driven by an external motor. Another LVAD pump developed by a company called “Impella” is believed to employ a similar method of vascular access but drives the pump with a miniature motor integral with the pump. Electrical power is supplied to the motor via a percutaneous wire.
Both of these LVAD systems noted immediately above are believed to maintain seal integrity with respective external fluid purge systems, but which are further believed to exhibit very limited durability. Neither system has been adapted to ambulatory or chronic use. It is believed that the period of use of these pumps has been limited to about two weeks.
Mechanical circulatory assistance has been shown to be an effective treatment for patients suffering from severe congestive heart failure (CHF). Both left ventricular assist devices (LVADs) and right ventricular assist devices have been adapted for bridging patients to heart transplantation and for long-term (destination) therapy. Unfortunately, existing methods for inserting these devices require major surgery during which the patient is placed on cardiopulmonary bypass and the heart may be arrested while vascular grafts are connected to a chamber of the heart to provide blood inflow to the pump of the assist system.
The implantation of existing LVADs carries too much risk to justify their customary use except in the most extreme circumstances. Current LVADs require a cardiovascular surgeon and cardiopulmonary bypass for implantation. Many previously disclosed devices and prior efforts require that both the abdominal cavity and the thoracic cavity be opened to implant the pump. Subdiaphragmatic placement of the pump necessitates diaphragmatic penetrations, which is desirable to avoid if possible.
Accordingly, left ventricular assist devices have previously been used only rarely in the treatment of CHF and then as a treatment of last resort. This is highly unfortunate, because LVADs offer greater hemodynamic efficacy than virtually all other adapted treatments, and also offer the potential of much greater clinical benefit in the treatment of congestive heart failure than other therapies and comparable to cardiac transplantation.
The substantial risk associated with present methods of implanting LVADs and RVAD has limited their use to end-stage patients. A much larger group of patients with less severe heart disease are not, presently, considered candidates for treatment with mechanical circulatory assist devices because of the substantial risk of implanting circulatory assist devices.
Thus, there remains a need for improved devices and methods that would permit less invasive cannulation of the chambers of the heart without the need for large incisions, cardiopulmonary bypass and the need to arrest the heart. This would make it possible to better serve large numbers of patients with less severe CHF.
The various aspects, modes, embodiments, and features of the present invention, as herein described, variously address certain existing needs such as just described, as well as others, in addition to overcoming and improving upon other shortcomings and deficiencies observed in prior efforts and previously disclosed devices.